The present invention relates to improved methods and apparatus for filling acetylene gas cylinders. More particularly, the present invention relates to improved solvents for use in porous mass acetylene cylinders.
Acetylene gas is widely used in industry, primarily for cutting, welding of steel members and as a heat treatment fuel. As is well known, however, acetylene gas is relatively unstable at high pressure and cannot be transported safely in open chambered cylinders of the type used to transport most other industrial gases. Due to this instability, acetylene is generally used and sold as "dissolved acetylene". That is, acetylene is normally transported in elongated steel cylinders of a specialized type, each cylinder containing a porous "body" or "mass" within which an acetylene solvent is absorbed. The porous mass normally fills the entire cylinder body, and typically comprises a porous, monolithic substance such as calcium medisilicate having an admixture of suitable fibrous material, for example asbestos, to increase its mechanical strength. In order to stabilize the acetylene to be added, the porous mass is charged or filled with a solvent. In typical prior art applications, the solvent was acetone or dimethylformamide (DMF).
While such a solvent charged porous mass enables the container to store a greater quantity of acetylene than can be otherwise safely stored, it is clear that the desirability of any one solvent over another is a function of the safety, cost and capacity of each individual solvent. Accordingly, a low cost, high capacity solvent with undiminished safety characteristics is highly desirable.
Due to the use of solvent charged porous mass cylinders, filling of acetylene cylinders involves an additional problem which is not normally encountered in the filling of cylinders with gases other than acetylene. When the acetylene gas is removed from the cylinder by the user, a certain amount of the solvent can escape along with the acetylene. As a result, the quantity of solvent remaining in a returned cylinder is generally always less than the initial charge. This, in turn, results in an additional cost associated with supplying acetylene in this manner since the cost of make-up solvent will ultimately be charged to the user.